In “Active Smart Cards”, extremely thin, flexible galvanic elements with a total thickness of, for example, less than 0.5 mm are used as energy stores. In the case of such thin electronic chip cards, the flat energy store is provided for supplying power to the IC chip or other components such as integrated miniature sensors or transponders.
Such a smart card must conform to ISO standards in its overall form comprising the card body, components and energy store in terms of being flexurally resistant in accordance with DIN-ISO 7816-1 and DIN ISO/IEC 10 373, i.e., the ISO bending test in accordance with DIN-ISO 7816-1 and the test specification in accordance with DIN ISO/IEC 10 373 must be satisfied. In the dynamic bending test, the card is flexed 2 cm in length and 1 cm in width with a frequency of 30 bends per minute (=0.5 Hz). In this test, a card must remain undamaged after at least 250 bends in each of the four possible directions (that is altogether 1000 bends). In the dynamic torsion test, the card is loaded ±15° about the longitudinal axis with a frequency of 30 bends per minute (=0.5 Hz). The standard demands 1000 torsions without the chip functionality failing or any mechanical damage being visible on the card.
In the previously used methods of hot and cold lamination, the metal housing of the element was often damaged so that the overall system of the card became unusable. If the housing was introduced into the chip card by cold lamination with known adhesives such as, for example, commonly used two-component polyurethane adhesives, cracks often occurred when the ISO bending tests were carried out.
EP 0 997 959 B1 describes galvanic elements with a non-aqueous electrolyte which have housings comprising laminate films. Such laminates generally comprise a composite aluminum foil coated on both sides, which can easily be deep-drawn to 5 mm and, on the basis of this property, immediately passes the ISO test. The plastic encapsulation thereby prevents tearing.
In DE 101 02 125.9, the mechanical reinforcement of an electronic chip card with a galvanic element arranged in it by means of a partial or complete coverage comprising metal or fiber-reinforced plastic is described.
A further possibility for stabilizing the metal housing is proposed in DE 102 26 848.7. In that application, in the case of a galvanic element with at least one lithium-intercalating electrode and a thin, flexible housing comprising two metal foils which bear directly against the electrodes and are connected to each other in sealed manner by means of an adhesive or sealing layer, at least one of the metal foils is provided on the outer side with a layer of plastic increasing the stability and strength, and an adhesive layer is arranged between the metal foil and the layer of plastic. Such a galvanic element must, however, be transformed into a laminated structure in further method steps.
It would therefore be advantageous to provide an active chip card which meets the high requirements in terms of mechanical stability with respect to flexural stresses and torsional stresses and which can be easily produced and is constructed from a few layers.